366 



SCIENCE 



[N. S. YoL. SLII. No. 1081 



A SIMPLE METSOD OF INDICATING GEO- 

 GSAPEICAL DISTBIBVTION 



There are two ways in whicli the distribu- 

 tion of plants and animals on the surface of 

 the earth may be expressed. The first is in 

 terms of countries or provinces or their sub- 

 divisions. To this there are several objec- 

 tions : (a) The boundaries of a country or 

 province or county are frequently very irregu- 

 lar and do not follow any definite direction. 

 These areas are, moreover, as a rule, very un- 

 equal in size. (6) The boundaries of countries 

 which have a different form of government are 

 unstable and are liable to change. This has 

 frequently happened ah-eady within the mem- 

 pry of men still living and is likely to happen 

 •again, in the near future, (c) The method is 

 ^only applicable to land areas. It can not be 

 .-applied to the fauna and flora of the oceans. 



The second method is one which has not 

 IbasnL Ktuch used so far but is much more scien- 

 tiSc and exact. It is that of indicating the 

 range of a plant or animal in terms of lati- 

 tude or longitude. However important inter- 

 national boundaries may be from the human 

 standpoint they have no meaning to plants 

 and animals — unless indeed they should happen 

 to coincide with some natural boundary, such 

 as a mountain range or an expanse of water. 

 But the parallels of latitude and the merid- 

 ians of longitude are so numerous that it is 

 difficult to remember the particular countries 

 traversed by any one of these in its course. 

 "While most people know that the forty-ninth 

 parallel forms the northern boundary of the 

 western half of the United States, very few 

 indeed could name the states traversed by the 

 fortieth parallel. 



The method suggested here is a modifica- 

 tion of the second of the above. It is proposed 

 to divide the whole earth's surface into a series 

 of areas bounded by the parallels and merid- 

 ians. Each of these areas will be more or less 

 rectangular, but only two of the four sides 

 will be actually parallel. The size of the areas 

 will gradually diminish towards the poles, but 

 those within the same latitude will be of equal 

 area. Each " merosphere " will have a definite 

 number attached to it and will be capable of 



division into smaller areas, each of these ulti- 

 mate units measuring one degree of latitude 

 by one degree of longitude. The size of these 

 proposed primary areas or " merospheres," as 

 I have called them, will be a matter for legit- 

 imate discussion. If too small they will be so 

 numerous as to have no advantage over the 

 method of expressing distribution in terms of 

 latitude and longitude. If, on the other hand, 

 they are too large they will be useless for indi- 

 cating distribution. The actual size proposed 

 here measures six degrees of latitude by nine 

 degrees of longitude. The reason for the 

 adoption of these figures is twofold. It is 

 true in a general sense that isotherms or lines 

 of equal mean temperature run for the most 

 part east and west unless where deflected by 

 mountain chains or sheets of water when they 

 may run in any direction, even north and 

 south. It is also true, in a general sense, that 

 the temperature falls steadily from the limits 

 of the tropical region towards the limits of 

 the polar regions. While there are wide varia- 

 tions in different continents, I have taken the 

 rate of fall as being on the average about 1J° 

 E. for every parallel of latitude. Six degrees 

 of latitude will therefore correspond to about 

 9° F. or 5° 0. 



If the width of the proposed areas were 6° 

 of longitude instead of 9° these areas in the 

 neighborhood of the equator would be approxi- 

 mately squares, but would be narrow towards 

 the poles. By making the width of the pro- 

 posed areas 9° instead of 6° squares will occur 

 about midway between the equator and poles 

 and the number of areas or " merospheres " 

 will be proportionately reduced. 



The details of the proposed scheme are as 

 follows : Beginning at the equator, the north- 

 ern half of the earth is divided into fifteen 

 parallel belts, each comprising 6° of latitude. 

 These are numbered consecutively from N 1 

 to N 15. The southern hemisphere is divided 

 similarly into belts S 1, S 2, etc. Each belt is 

 divided into 40 divisions beginning at the 

 meridian of Greenwich, the numbers running 

 consecutively westwards until the meridian of 

 Greenwich is again reached. As mentioned 

 above, each division comprises 9° of longitude. 



